The present invention relates to a new and improved apparatus for controlling turning movement of steerable vehicle wheels.
It has previously been suggested that steerable wheels of a crop harvesting vehicle be controlled in response to either manual rotation of a steering wheel or changes in a sensed relationship of the vehicle to an edge of a crop grown in a row planted plot or otherwise distinguishable from the surrounding vegetation. During steering of the vehicle in response to manual rotation of the steering wheel, an electronic control unit is operable to actuate a steering control valve to direct high pressure fluid to a power steering motor. During automatic steering of the vehicle in response to changes in the relationship of the vehicle to a crop, the electronic control unit is operable to actuate the steering control valve in response to a sensor unit.
During automatic steering of the vehicle, the sensor unit continuously measures the distance from the vehicle to an edge of the crop plot. The output from the sensor unit is transmitted to the electronic control unit. In response to the output from the sensor unit, the electronic control unit effects operation of the steering control valve to turn the steerable vehicle wheels to maintain a constant relationship between the vehicle and a portion of the crop to be harvested as the vehicle moves forward.